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AN
Inaugural Experimental DhTertation
ON
DIGESTION,
SUBMITTED TO THE EXAMINATION OF THE
tier. JOHN E WIN G, 'S. T. P. P*orosrs
THE
Trustees and medical faculty
OF THE
UNIVERSITYoF PENNSYLVANIA,
On the 17th day of May, 1796.
FOR THE DEGREE OF DOCTOR OF MEDICINE.
By yohn TVilfon, A. M. of Penn/y/vania,
MEMBER OF THE PHILADEDHHIA MEDICAL SOSIETY.
Aggrediar, non tam perficiendi, quam experiendi voluntate.
Cic. 0*at. ad Brut.
FHllADELTHIA,
PRINTED BY LANG Is* USTICh\
\ M.DCC.XCVI.
^ C -
TO
Cajpar TViJlar, m. d.
ADJUNCT-PROFESSOR OF ANATOMY, SURGERY,
AND MIDWIFERY,
IN THE
UNIVERSITY OF PENNSYLVANIA;
THIS DISSERTATION
IS RERPECTFULLY INSCRIBED,
AS A SMALL TRIBUTE OF GRATITUDE AND ESTEEM,
BY BIS MUCH OBLIGED FRIEND AND PtfPllj
JOHN WILSON.
e_
Introdu&ion.
OlNCE the works of a Fordyce, a Hunter,
and, above all, the ingenious Spallanzani have ap-
peared on this fubject, a further inveftigation feemed
unneceflary; but as phyfiologifts were not fettled in
their opinions, and as fome ufeful experiments have
heretofore been neglefred, which might have a ten-
dency to throw fome light on fo interefting a fubje£t,
this fmall attempt may not prove unacceptable.
But notwithstanding this, I am laid under an ob-
ligation of an higher nature j as the laws of this Se-
minary require that every candidate for medical
honours ihould exhibit before the Truftees and Fa-
culty, fome evidence of his improvement in the
principles cf that art which has been the ground of
his ftudies; therefore, neceffity, not choice, prompts
the unexperienced Student to attempt the inveftiga-
tion of fomething new, or take the tedious round of
dull repetition—The former enfuring upon his unde
15
( 6 )
fended head the piercing ftiaft of criticifm, while the
latter is fure to create difguft.
In a fubjeft fo difficult and obfcnre as the animal
ceconomy, it is not furprifing, that philofophers fliould
be fo often embarraffed; and that inftead of certainty,
they fliould frequently be obliged to determine her
operations by a feeming probability, or by a vague
and diftant analogy.
All animated beings feem to be fubjecl: to certain
laws calculated for the purpofe of their ceconomy.
Thefe laws difpofe them to certain modes of action,
which occafion a diminution either of their fluids, or
folids, or both.
Poflibly they may remain in a dormant ftate for
fome time without fuftaining any diminution or lofs of
fubftance. But when a lofs is fuftained, it is necef-
fary, that it fliould be fupplied by the addition of
fome new matter. If this matter is different in its
qualities from the matter of the body which is loft, it
is neceffary that it fliould undergo fome charjge, and
be converted into a fubftance endued with the fame
qualities, as that which was loft.
Befides the continual wafte which animals are
fuffering, there is a certain period of their lives in
( 7 )
which they are acquiring new parts, and encreaung
thofe already formed. In confequence of this, it is
necefTary that food fliould be employed to fupply mat-
ter for this formation and increafe.
For this purpofe, there is a certain procefs in the
organs of digeftion of living animals, through which
food has to pafs, before it can be animalized and get
into the general fyftem of veffels. It muft, therefore,
be prefumed, that food has to undergo fome change,
in confequence of its delay in thofe organs.
Although the Organs of Digeftion in different
animals are fo various, it is moft probable, that thofe
changes which take place in the food of different
animals are fimilar ; their mode of life only rendering
a different apparatus necefTary.
But our prefent enquiry is not about the fituation
and ftru&ure of thofe organs, or the quantity or
quality of food beft adapted to them ; it is about the
mode of aflimilating thofe fubftances to an animal
nature, whereby a frefti growth of parts may be
maintained, or a conftant lofs of fubftance renewed.
A N
JNAUGURAL DISSERTATION
O N
DIGESTION.
X HE human frame, like every other machine,
Would necefTarily wear out by the mutual attrition of
its parts, without a conftant renovation. For this
purpofe we are endued with the peculiar appetites of
hunger and thirfi. The difagreeable fenfations ari-
fing from a non-indulgence of thefe, and the extreme
pleafure produced by their gratification, ftimulate us
to take in alimentary fubftances; and thefe having
gone through the procefs of digefiion, are converted
into fit nutriment to fupport .the various parts of the
body.
The fubftances beft adapted to this purpofe are
taken from the animal and vegetable kingdoms.
Thefe, under various forms and modifications, con-
( io )
ftitute the proper food for the body. But the mode
of operation in the procefs of Digeftion, has been a
fubje& of confiderable aliercation among phyfio-
logifts.
Some phyfiologifts have afTerted that the ftomach
operates in digeftion principally by a triturating
power. Another opinion concerning Digeftion was,y
that it is effe£ted by fermentation.
Since the experiments of the ingenious Spallan-
zani, mechanical agency, by trituration, in the pro-
cefs of Digeftion, has no longer any weight among
philofophers. It remains, then, to confider what
chemical change really does take place, whereby fuch
heterogeneous fubftances are reduced to one fimple
homogeneous matter, called chyle. This change has
been afcribed either to fermentation, or folution, pr
both.
The do&rine of fermentation was much in vogue
about the middle of the laft century, when an expla-
nation of the various functions of the human body
was fought for in fermentation. It appears that
Boerhaave firft oppofed the generally received opi-
nion of fermentation in the animal functions, but ftill
admitted a limited degree of it in the aft of Digeftion.
He fuppofes that nothing prevents a compleat fer-
( " )
mentation of the food taking place in the ftomach,
but its fhort continuance there. Some modern phy-
sicians, viz. Pringle and M'Bride, think this limitation
too great, and maintain that a compleat fermentation
really does take place in the procefs of Digeftion.
But let us take notice that their experiments were
made out of the body, and their conclufions drawn
from its being produced in this fltuation by adding
faliva to alimentary fubftances. Dr. Rufh alfo appears
to conclude in favour of this latter opinion from the
like experiments, as well as thofe made in his own
ftomach.
Indeed, when we confider the circumftances of
the food during Digeftion, there certainly is a ftrong
prefumption in favour of this doftrine. But notwith-
ftanding this, and the nearly convincing arguments
of fuch ingenious advocates, I am led to adopt a con-
trary opinion from my own experiments, and thofe
of others. Befides, the continual influx of frefh
humours into the ftomach, and the fhort continuance
of alimentary fubftances there, ftrongly induce me to
believe that it is not a fermentative procefs.
The different fpecies or ftages of fermentation, as
defcribed by chemifts, are the vinous, acetous, and
■putrefactive. The putrefactive ftage of fermentation,
few, or none, now believe to have any agency in
( ■* )
Digeftion. On the contrary, from a variety of expe-
riments made to afcertain this faft, I found that pu-
trid aliment is incapable of being converted into
chyle before it is fweetened by the action of the
gaftric juice upon it. Thofe who argue in favour of
the vinous and acetous ftages of fermentation, main-
tain their opinion from particular phenomena fre-
quently attending the procefs of Digeftion; fuch as
acid eru&ations and vomitings, the acid tafte of the
gaftric juice, and internal coat of the ftomach, &c.
That fuch appearances frequently do take place
cannot be denied; but whether they are the natural
effects of the digeftive procefs, or unnatural incidental
occurrences, owing to a morbid ftate of thofe organs,
or to an improper quality or quantity of food, is a
matter of contention. To the latter opinion I am
ftrongly inclined, both from experiments and other-
wife.
To difcover whether the quality of food has any
influence on the digeftive organs, I fed a number of
dogs, for fome time, on animal food alone. They
were then killed about four hours after eating frefli
animal fubftances, at which time Digeftion was con-
fiderably advanced j but neither the gaftric juice of
thofe animals, or the contents of their ftomachs
fhewed any flgns of acidity when touched with an
( *3 )
infuflon of blue vegetables. According to thofe expe-
riments, animal fubftances which feem to be the moft
natural food of thofe animals, do not produce the lead
acidity in the digeftive organs in a healthy ftate, and
ftill digeftion was completely performed. But as uni-
formly as I fed them with vegetable, or with animal
and vegetable fubftances together, I found an acid
to exift in the ftomach and duodenum of thofe animals.
I alfo made a number of other experiments differently
modified, and they uniformly rendered flmilar refults.
Mr. Hunter very properly obferves, " That fer-
mentation can go on in the ftomach, there is no
doubt; but when this ha ipens, it arifes from the
powers of digeftion being defe&ive." Animal Eco-
nomy, p. 161.
And again, the fame author fays, " That it may
be admitted as an axiom, that two procefTes cannot
go on at the fame time, in the fame part of any fub-
ftance ; therefore, neither vegetable nor animal fub-
ftances can undergo their fpontaneous changes, while
digeftion is going on in them ; a procefs fuperior in
power to that of fermentation." P. 163.
Having found, by the former experiments, that an
acid is not necefTarily produced in digeftion, I made
a number of experiments out of the body with water,
C
( H )
faiiva, and the gaftric juice, in di&rent alimentary
mixtures, to find at what time fermentation really
does begin.
Experiment I Equal parts of boiled pork, parfoip
and leavened bread, were put into two vials. In one
vial water alone was added to thefe fubftances ; in
the other equal parts of fajiva, and water. Thefe
mixtures were fubmitted to a fand heat equal to the
human body. No fermentation was difcovered tili
between four and five hours. Air-bubbles firft ap-
peared' in the vial, containing faiiva.
Experiment II. Leavened bread and boiled pork
were put. into two vials. In one vial water was adr
ded, and in the other faiiva. Thefe w£re fubmittcd
to a heat equal to the human body ; but in neither of
thefe could fermentation be difcovered till towards
five hours, either by the cfcape of air-bubbles, or by
an infufion of blue vegetables.
Experiment III, Unleavened bread, roafled beef
and potatoe in equal quantity were put into two vials.
In one vial water, and the other faiiva, and water were
added to thefe mixtures. They were then fubmitted
to a fand heat between 960 and 1120 of Fahren-
heit's thermometer. A faiall .degree of fermentation
was-perceived at the end of four hours. The reafoa
( 15 )
of fermentation beginning fooner in this experiment,
than in the former, may be accounted for from the
heat being fomething greater than that of the human
body.—The vials containing water alone in the fore-
going experiments, were ufed only by way of compa-
"rifon, and the chief difference appeared to confift
in the efcape of air-bubbles, and not in the change of
colour produced by an infufion of blue vegetables.
Experiment IV. I obtained a quantity of pure
gaftric juice from my own ftomach. This I mixed with
equal quantities of faiiva and water in fimilar mix-
tures with the former experiments, and fubmit-
ted them to a heat equal to the human body. They
remained much longer than any of the former expe-
riments before they fliewed any figns of fermenta-
tion. The gaftric juice, in thofe experiments, mewed
as ftrong antizymic powers as it had done, in former
experiments, antifeptic ; and both powerfully oppofe
the doctrine of fermentation, either putrefactive or
acetous*, in the procefs of digeftion.
Finding that little difference took place, in the
former experiments, between alhnentary mixtures
with water and thofe with faiiva, I was induced to
believe that any other fluid of the body of equal
viilklity (the gaftric juice excepted) would (hew figns
of fermentation with any alimentary matters, as foon
( 16 )
as with faiiva. I therefore made a number of expe-
riments with the ferum of blood alone, and mixed
with water, in different preparations, under fimilar
circumftances with the former experiments ; but was
never able to difcover any difference, either by the
efcape of air-bubbles, or when touched with an in-
fufion of blue vegetables.
I am, therefore, cf opinion with Dr. Fordyce, in
oppofition to Dr. M'Bride, that the faiiva has no fer-
menting principle ; and he very juftly obferves, that
" Dr. M'iiride grounds his opinion on experiments
made with pieces of meat and water mixed together
alone, and pieces of meat, water and faiiva mixed
together in fimilar vials; upon letting them ftand,
air-bubbles were found in the vial, in which the meat,
water and faiiva were contained, before there were any
found in the vial, in which the pieces of meat and wa-
ter were alone contained. The refultwasthe fame when
bread and water ; and bread, water and faiiva were
compared : and alfo, when bread, meat and water ;
and bread, meat, water and faiiva were compared.
But no deduction can be made from thefe experi-
ments, by which the power of the faiiva to induce
fermentation can be grounded; becaufe the faiiva
giving vifcidity to the water would prevent vapours
from rifing in fmall and imperceptible bubbles j and
( *7 )
would retain them until they became more numerous,
and until they united together fo as to become more
fenfible." Eordyce on Digeftion, p. 53&54-.
It may be affced, at what time does Digeftion
begin to take place.? From a number of experiments
made on dogs to afcertain this point, I found it to be
immediately after food had been taken into the fto-
mach. Now we know that fermentation cannot take
place in any known circumftaces out of the body in
lefs than four or five hours, when a ferment is not
added, in which time the whole procefs of digeftion is
completed. That fermentation may take place to-
wards the latter end of digeftion, will not be denied;
but this is far from being a necefTary confequence to
digeftion, as Dr. Rufli fuppofes : it is nothing more
than an accidental circumftance necefTarily taking
place from food being too long retained in the fto-
mach, when the power of the digeftive organs has
been too feeble to affimilate it, before this natural
change takes place.
To put the fubjeft beyond a1! poflibility of contro-
verfy, I inftituted a number of experiments hereto-
fore untried, and which were as difagreeable as new.
Experiment I. Having breakfafted upon coffee,
leavened bread and butter, and a little boiled ham,
( i8 )
fcymyofrelifti—four hours afterwards, I took ah
Emetic, which brought up the contents of my ftomach.
Thefe I fubmitted to diftillation and re-diftill uion,
feveral times repeated; but I could not difcover the
Itnalleft appearance of fpirit of wine throughout any
part of the procefs.
Experiment II. Having dined upon roafted beef,
leavened bread, potatoes and water—three hours
after I took three grains Of emetic tartar, and threw
tap the contents of my ftomach. This appeared acid
to the tafte, and imparted a flight red colour to a
blue infufion of vegetables, as Dr. Rufh very juftly
remarks in his experiments ; but after fubmitting
thefe to diftillation, as in the former experiment, I
could not produce any figns of fpirit of wine.
Thefe experiments, though extremely difagreeable
I repeated at a time when I enjoyed the moft per-
fect ftate of health, and with exadrdy the fame
iffue.
Experiment III. But left it fhould be thought that
the experiments made on my own ftomach were not
fufiicient to eftablifh the doctrine, I obtained the fa-
vour of a healthy man in the Houfe of Employment to
aflift me. He dined heartily on leavened bread,
boiled pork, parfnip and potatoe, and a little water
( >9 )
by way of drink. Thijee hours after he difchsffged
the contents, of his ftomach by an emetic,
Experiment IV. The fame man having dined
upon leavened bread, beef-ftake and molaffes been—•
four hours afterwards he took an emetic, and threw
up the contents of his ftomach. The two laft expe-
rements were* treated by diftillation, fimilar to thofe
made on my own ftomach, and with exactly the. feme
refult.
Thefe experiments appeared fufficient to difprovo
the doctrine of fermentation in the procefs of DigeC
tion. Neverthelefs, if,the fpirit of wine fhould accident
tally appear in diftilling the contents of the ftomach*
I could not fubfcribe to the doctrine of fermentation
necefTarily having any agency in Digeftion.; becaufe
the digeftive organs may be fo flightly debilitated, or
be under fo fiaall a degree of morbid excitement, as
fcarcely or not at all to be perceived; and under thefe
circumftances fermentation of a vinous nature might
readily take place. This is a ftate, every perfon is
very fenfible, frequently takes place in his ftomach ;
but who, under fuch circumftances,. would ever, fup-
pofe. this to be either natural or asceflkry to di-
geftion .?
( 20 )
In this manner I would account for an acid be-
ing produced in the ftomach, when an acetous acid
is generated there. Eut, is the acid moft commonly
found in the ftomach, the pure acetous, acid ? Is it
not more properly called the phofphoric acid, which
is evolved in the time of digeftion, or otherwife the
carbonaceous matter of the faccharine part of the ali-
mentary mixture ftrongly attracYmcv pure oxigene,
forming thereby carbonic acid, fo frequently found in
the ftomach ?*
Now, feeing- we fo conftanfly obferve that fer-
mentation, combuftion, and elective attraction pro-
duce new and different changes in bodies indepen-
dent of each other ; may we not confequently look
for other changes to take place in the properties of
bodies entirely different from either ? This we fee in
the procefs of Digeftion, whereby two or more fub-
ftances are decompofed, and re-combined in another
* After having written the above pages, I met with the follow-
ing Letter de M. Reynior, a M. de la Metherie.
The writer cf this letter informs M. de la Metherie, that pro-
feflbr Struve and M. Maquart, have difcovered that the phofpho-
ric acid and volatile alkali are the two eflential conftituent parts of
the gaftric juice ; and M. Struve has compofed a liquor which ads
on alimentary matters, in the fame manner as the gaftriq juice.
Journal de la Phxfiyvc,
C ai )
manner by a procefs fui generis, and thereby forming
a tertium quid, poffeffing properties widely different
from its conftituent principles. And, as Mr. Hunter
obferves, "The procefs of Digeftion differs from
every other natural operation in the change of bodies.
It is by no means fermentation, though it may fome-
what refemble it. For fermentation is a fpontaneous
procefs, and is that natural fucceflion of changes, by
which vegetable and animal matter is reduced to
earth; therefore, mild be widely different from
Digeftion, which converts both animal and vegetable
fubftances into chyle; in the formation of which,
there cannot be a decompofition fimilar to fermen-
tation.
" Digeftion is very different from chymical folution,
Which is only an union of bodies by elective attrac-
tion, not a real change of the fubftances themfelves,
but of their properties. But digeftion is an aflimila-
ting procefs, and in this refpect. is fomewhat fimilar in
its action to morbid poifons. It is a fpecies of gene-
ration, two fubftances making a third ; but the curi-
ous circumftance is its converting both vegetable and
animal matter into the fame kind of fubftance or com-
pound, which no chymical procefs can effecl:."
A queftion may ftill be afked, whence is the acid
principle derived which cxifts in the fecretions, par-
( 22 )
iicularly in the Urine, if a fermentative procefs is not
admitted in the aft of Digeftion ? To this I anfwer,
that all the fecretory organs of the living body appear
to pofTefs a power peculiar to themfelves. And is it
not an immutable law in animal bodies, that each
gland can fecrete no other, but its own proper fluid,
which is wholly, or in part, fabricated in the very
gland itfelf, by an animal procefs, which it there
undergoes ? But why one gland poffefies the power
of fecreting a faltifli, another a bitterifh, or another
an acid principle, is a difficulty with which the pre-
fent ftate of Phyfiology has not made us acquainted,
Neverthelefs, we know that all the fecretions of the
body are produced from the peculiar matter of blood
fpecifically acred upon by the various fecretory organs,
They cannot be produced by any other fubftances,
or powers, either within or without the body,
In endeavouring to explain the modus operandi in
the procefs of Digeftion, we fliould conftantly re-
member this one principle, that nothing can be cre-
ated or annihilated in all the proceffes and operations
of nature or art. Neverthelefs, we might almoft be
led to a contrary conclufion from obferving the great
difference in appearance between aliment before and
after the procefs of Digeftion,
( n )
Aliment contains all the elements of chyle as yd\
before as after Digeftion, but in a different ftate of
combination. Mr. Boyle has proved that the proper-
ties of compound bodies depend upon their principles
of combination, and not upon the properties of their
elements. For inftance, barley and fugar are' com-
pounds of different properties, but by diftillation they
yield fimilar elements. In like manner a piece of
mufcle pafling through the organs of digeftion pro-
duces chyle: now the mufcle and chyle are found by
chymical analyfis to yield the fame produces. It ap-
pears then, that the mufcle and chyle differ from
each other only in their mode of combination. TJje
converfion, therefore, of a mufcle into chyle, is
a feparation of its elements, and a recombination of
them in a different manner ; fo that the new com-
pound fhall have new properties,
If the changes above mentioned depend upon
elective attraction; a queftion may arife, why cannot
chyle be produced at any time out of the body, by
giving an opportunity for this attraction to a&, or
why animal and vegetable fubftances do not always
exjfi in the form of chyle ?
I anfwer, that when two fubftances have a difpo-
fition or power to unite with or decompofe one ano-
ther, it is not fufficient that they fhould merely
( «4 )
poflefs the propenfity or even ability of producing the
effeft, but likewife be in fuitable circumftances for
that power to aft. Thus, for example,- a folution of
fugar and water kept in a temperature not exceeding
400 of Fahrenheit's thermometer, will not have its
elements to feparate and recombine into wine, but if
otherwife, this effeft will be produced.
In this manner the aftion of the living ftomach,
and other organs of digeftion, upon the food, are
indifpenfably necefTary, in order that thofe powers
may aft, by which a new ftate of aggregation may be
effefted.
Food placed in all the chymical circumftances
fimilar to thofe in which it is placed in a living fto-
mach, would never be converted into chyle, but
would undergo other changes totally different. Ani-
mal food would putrefy, and vegetable food would
become acid. If the living power of the ftomach be
ftrong and healthy, food will be perfectly digefted;
but if weak, it will go imperfectly through the
organs of digeftion, and fome part of it will necefTa-
rily undergo thofe changes which it would have
undergone in fimilar chymical circumftances; but
will not be then afted on by the living organs of
digeftion.
( *5 )
For want of this circumftance, chyle never can
be produced in any other place than in the organs of
digeftion of a living animal. The peculiar ftate of
the food produced by the aftion of the living ftomach,
without which chyle cannot be formed, is illuftrated
by the following chymical faft, viz. Farinaceous
matter, mucilage and native vegetable acid, may be
combined into wine; but as an indifpenfably neceffary
pre-requiflte, they muft be formed into fugar. What-
ever may be the reafon or neceflity for this, it is not;
eafy to demonftrate ; but moft certainly, it is a caufa
fine qua non. Juft fo the food is brought into a .ftate
indifpenfably necefTary in the living organs of digef-
tion, previous to the formation of chyle,
FINIS.
heoL. Hist,
VslZ.
nn
^M
ft:#
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